1. Technical Field of the Invention
The present invention relates to memory devices, address decoders and related methods.
2. Description of Related Art
As is known, integrated circuits are used in a wide variety of electronic equipment, including portable, or handheld, devices. Such handheld devices include personal digital assistants (PDA), compact disk (CD) players, MP3 players, digital video disk (DVD) players, AM/FM radios, pagers, cellular telephones, computer memory extensions (commonly referred to as thumb drives), etc. Each of these handheld devices includes one or more integrated circuits to provide the functionality of the device. As an example, a handheld audio player may include multiple integrated circuits to support the decoding and playback of stored audio files in order to produce an audio output that is delivered to the user through speakers, headphones or the like. Such integrated circuits include processing devices that execute a program that includes a sequence of instructions and/or data that are stored in a memory device such as a random access memory (RAM) or a one-time writable memory such as read-only memory (ROM).
When electronic devices are constructed, it is desirable to perform operational tests of components such as integrated circuits prior to assembly. Once an integrated circuit is mounted on a printed circuit board, if a defect is found, it can be costly and time prohibitive to remove the device from the board to install a new component. One-time writeable memory devices provide a challenge to test. Certain tests can be performed to test the integrity of the chip, however, a test of the read and write operations of the device require the memory cells to be burned (programmed) in a non-reversible fashion. Tests that are performed, prior to programming, must be limited in nature. In particular, the amount of memory tested must be limited to leave adequate space for programming.
One solution to this problem is to test a single row or column of a ROM prior to programming. A row or column is written with a test pattern and then read to determine of the memory device is properly functioning. If the device passes, the remaining memory cells are programmed after the device is installed. However, errors present in other portions of the memory cannot be detected.
A need exists for a memory device, particularly a one-time writable memory, that can be effectively tested and efficiently implemented in an integrated circuit.